1. Field of the Invention
The present invention relates to an electrophotographic photoconductor having a high resolution and photosensitivity, low residual potential and excellent electrostatic property and a method for producing the electrophotographic photoconductor, and an image forming apparatus and a process cartridge used for the image forming apparatus by using the electrophotographic photoconductor.
2. Description of the Related Art
In recent years, image forming apparatuses such as laser printers and digital copiers using an electrophotographic system, provide an image with improved image quality and stability and are broadly used. Recently, speeded-up, downsized, and full-colored image forming apparatuses are rapidly developed, and an electrophotographic photoconductor (hereinafter, referred to as a photoconductor) used for the image forming apparatuses, is needed to improve further carrier mobility and photosensitivity, and reduce residual potential.
The electrophotographic photoconductor used in the image forming apparatuses, which uses organic photosensitive materials, are commonly generally applied in terms of cost, productivity, environmental safety and the like. In terms of a layer configuration, the electrophotographic photoconductors are broadly classified into a single layer photoconductor having charge generating ability and charge transporting ability in a single layer, and a laminated photoconductor having layers functionally separated into a charge generating layer having charge generating ability and charge transporting layer having charge transporting ability. The latter is generally used in terms of the electrostatic stability and durability.
A mechanism of forming a latent electrostatic image in the laminated photoconductor is that the photoconductor is charged and irradiated with light, in which the light passes through the charge transporting layer and is absorbed by the charge generating material in the charge generating layer so as to generate charge. The generated charge are injected into the charge transporting layer at an interface between the charge generating layer and the charge transporting layer, and move in the charge transporting layer by electric field, reach the photoconductor surface, and neutralize surface charge imparted by charging so as to form the latent electrostatic image.
In the laminated organic photoconductor, the reduction of resolution, photosensitivity, and charge mobility, and rise of residual potential are recognized as big problems for improving image quality and speeding-up the image forming apparatus.
The reduction of the resolution may be caused by that the charge are horizontally diffused to the substrate.
Additionally, the reduction of photosensitivity and the charge mobility and rise of the residual potential may be caused by that the charge are trapped in a process of moving by hopping in the charge transporting material.
To solve these problems, the following conventional arts are known: for example, crystal materials having charge transporting ability (Japanese Patent Application Laid-Open (JP-A) Nos. 9-132777, 2001-348351, 2001-302578, 2000-347432, 11-305464, 11-087064, 2003-073382, and 11-338171), organic magnetic materials (Japanese Patent (JP-B) No. 3045764), and polysilanes (JP-A Nos. 10-133404 and 9-114114) used as a charge transporting material, and these orientation are controlled to improve resolution and photosensitivity.
The charge transporting material may be oriented by magnetic field, electric field, rubbing process, vapor deposition and the like. However, the charge transporting materials used for these conventional arts do not satisfy electrophotographic property, and have not been practically applied.
Moreover, in addition to the above objects, the following techniques are known in a field of the electrophotographic photoconductor: a magnetic material contained in a surface layer is oriented for the purpose of improving wear resistance (JP-A No. 10-020536 and Japanese Patent Application Publication (JP-B) No. 5-049233); and a magnetic powder in the undercoat layer is oriented by magnetic field for the purpose of improving a smoothing property of an undercoat layer (JP-A No. 61-124952).
However, these techniques may be effective for improving the wear resistance and smoothing property of the undercoat layer, but not actually effective for essential properties for improving image quality of the image forming apparatus, such as resolution, sensitivity, residual potential, and mobility, these are rather sacrificed.